This application is based on Japanese Patent Applications No. 2001-297275 filed on Sep. 27, 2001, and No. 2001-346241 filed on Nov. 12, 2001, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle air conditioner having a heat pump refrigerant cycle which can switch one of a cooling operation and a heating operation.
2. Description of Related Art
In a heat pump refrigerant cycle capable of switching one of a cooling operation and a heating operation, decompressed refrigerant is evaporated in an interior heat exchanger by absorbing heat from air to be blown into a passenger compartment, and the absorbed heat is radiated to an outside air in an exterior heat exchanger, when the cooling operation for cooling the passenger compartment is performed. On the other hand, when the heating operation for heating the passenger compartment is performed, decompressed refrigerant is evaporated in the exterior heat exchanger by absorbing heat from outside air, and absorbed heat is radiated to air to be blown into the passenger compartment.
In this heat pump refrigerant cycle, during the cooling operation or a defrosting operation, because the interior heat exchanger is used as a cooling unit for cooling air, condensed water adheres on the surface of the interior heat exchanger. Accordingly, when the operation of the heat pump refrigerant cycle is switched from the cooling operation or the defrosting operation to the heating operation, the interior heat exchanger is heated, and condensed water adhering on the surface of the interior heat exchanger is evaporated. In this case, air having a high relative humidity is blown into the passenger compartment, and a windshield is readily fogged.
To overcome this problem, the applicant proposes a vehicle air conditioner in U.S. patent Application Publication No. 2001-0035286. In the vehicle air conditioner, when the operation of a refrigerant cycle is switched from the cooling operation or the defrosting operation to the heating operation, heating capacity of the interior heat exchanger is set smaller so that condensed water adhering on the surface of the interior heat exchanger is slowly evaporated. However, while the heating capacity of the interior heat exchanger is set smaller, a sufficient heating cannot be obtained in the passenger compartment.
In view of the above-described problems, it is an object of the present invention to provide a vehicle air conditioner which prevents a windshield from being fogged while restricting heating capacity from becoming smaller.
According to the present invention, in a vehicle air conditioner, a heat exchanger of a heat pump refrigerant cycle is disposed in an air conditioning case, for performing a heat exchange with air to be blown into a passenger compartment of the vehicle. The heat exchanger is disposed in the air conditioning case to form a bypass passage through which air flows to a downstream side while bypassing the heat exchanger. When a defogging mode is set in the vehicle air conditioner, air mainly passing through the bypass passage is blown toward a first area in the passenger compartment, near a windshield of the vehicle, and air mainly passing through the heat exchanger is blown toward a second area in the passenger compartment, separated from the windshield. Here, the defogging mode is generally set when it is determined that the windshield tends to be fogged. For example, when the operation of the heat pump refrigerant cycle is switched from the cooling operation, a defrosting operation or a dehumidifying operation to a heating operation, the defogging mode is set. Accordingly, even when the heating capacity of the heat exchanger is made maximum, by setting the defogging mode, it can restrict air having a large water vapor from being blown toward the windshield. Thus, it can restrict the windshield from being fogged while restricting heating capacity for heating the passenger compartment from becoming smaller.
Preferably, at least in the defogging mode, outside air outside the passenger compartment is mainly introduced into the bypass passage. Because outside air having low humidity can be blown toward the windshield through the bypass passage, it can further prevent the windshield from being fogged.
In the vehicle air conditioner, a partition member is disposed for partitioning the air passage within the air conditioning case into a first passage through which outside air outside the passenger compartment flows into the passenger compartment, and a second passage through which inside air inside the passenger compartment flows into the passenger compartment. In addition, the bypass passage is provided in the first passage. Accordingly, the heating capacity for heating the passenger compartment can be increased, while it can further prevent the windshield from being fogged.
Preferably, in the defogging mode, at least a part of air passing through the heat exchanger is discharged outside the passenger compartment from the air conditioning case, at least for a predetermined short time. Therefore, it can prevent air having a large water vapor from being introduced into the passenger compartment. In this case, the air passing through the interior heat exchanger, having the larger water vapor, can be discharged outside the passenger compartment from the air conditioning case through a drain port for draining water in the air conditioning case to an outside, or through a discharge port different from the drain port, in the defogging mode.